The invention relates to a kit for implanting a cementable endoprosthesis according to the preamble of claim 1.
Document DE 195 18 391 A1 discloses a proximal centering and sealing element for implanting a cementable endoprosthesis shaft, which element on the one hand serves as a proximal centering aid and on the other hand prevents escape of the cement in the proximal direction, as a result of which, when inserting the endoprosthesis shaft into the medullary cavity, there is an increase in the pressure of the bone cement located therein.
This known combination of endoprosthesis shaft and suitably adapted centering and sealing element has the disadvantage that the depth of insertion of the endoprosthesis shaft in the medullary cavity of the femur in the proximal-distal direction can be set only with difficulty and therefore inexactly. In addition, the centering and sealing element has only a limited sealing effect and inadequate centering in the medial-lateral direction.
The object of the present invention is to make available a set of instruments permitting more precise implantation of a cementable endoprosthesis shaft.
This object is achieved by means of a kit having the features of claim 1. Dependent claims 2 through 17 relate to further advantageous embodiments of this kit.
The object is achieved in particular by means of a kit for implanting a cementable endoprosthesis, comprising a fitting instrument and at least two components to be implanted, namely an endoprosthesis shaft and a proximal centering and/or sealing element, the shaft and the fitting instrument being designed to be able to be coupled to each other, and the centering and/or sealing element being designed to be placeable on the shaft and to be displaceable in the direction of extension of the latter, and either the fitting instrument comprising a limit stop part which forms a limit stop relative to the centering and/or sealing element, or a marking being arranged on the fitting instrument and on the shaft in order to ensure a defined mutual position between the centering and/or sealing element and the shaft.
This embodiment according to the invention has the advantage that the depth of fitting of the endoprosthesis shaft in the medullary cavity of the femur can be adjusted even during implantation. Therefore, it is still possible during implantation to adjust, for example, the length of the femur or depth of fitting of the endoprosthesis shaft in such a way that after the operation has been completed, both legs are the same length. In a preferred embodiment, the kit comprises a manipulating instrument which is inserted into the medullary cavity of the femur before fitting the shaft, in order to determine the optimum depth of fitting, so that in particular an optimum leg length or optimum ligament tensioning is achieved. The optimum depth of fitting which is determined in this way is read off and the endoprosthesis shaft is then inserted into the femur corresponding to this depth of fitting.
The proximal centering and/or sealing element has, in the proximal area of the femur, the task of centering the endoprosthesis shaft in the medullary cavity or sealing off the gap between medullary cavity and shaft, in order to ensure that the bone cement located in the medullary cavity cannot flow out, or of providing centering and sealing at the same time. This centering and sealing element which ensures both centering and sealing is preferably adapted in design to the geometry of the shaft in such a way that a displacement of the shaft along the sealing element in the distal direction is possible while maintaining the sealing effect.
The centering and sealing element can be placed on the resected femoral neck and can be inserted at least partially into the medullary cavity in the proximal area thereof so that the endoprosthesis shaft to be inserted subsequently is inserted in the medullary cavity with all-round centering, the element additionally exerting a sealing effect so that the bone cement located in the medullary cavity is prevented from escaping.
In an advantageous embodiment, the proximal centering and sealing element consists of a sleeve-shaped body extending in a proximal-distal direction, the body having two broad-side boundaries and two narrow-side boundaries which enclose an essentially rectangular inner space, and the two broad-side boundaries each forming inner side surfaces extending essentially parallel in the proximal-distal direction. This centering and sealing element is especially suitable for endoprosthesis shafts of blade-type design whose broad sides extend approximately parallel in the proximal-distal direction. In this way, a particularly good sealing effect is achieved between the centering and sealing element and the endoprosthesis shaft. A centering and/or sealing element is designed as a sleeve-shaped body whose inner space, in an advantageous embodiment, is designed such that a movement of the shaft in the proximal-distal direction is also possible during implantation of the endoprosthesis shaft. If this is desired, then the shaft would be able to settle even some time after implantation since the movement in the proximal-distal direction is not impeded.
The centering and/or sealing element advantageously consists of a polymerized bone cement, in particular polymethyl methacrylate (PMMA). During implantation, this centering and/or sealing element binds chemically to the bone cement present to form a particularly homogeneous connection. However, the centering and/or sealing element can also consist of another material, in particular of a metal such as a biocompatible titanium alloy.
The centering and/or sealing element satisfies either a centering or a sealing function, or both functions simultaneously, said functions being:
to center the shaft in the proximal section of the medullary cavity;
to guide the shaft centrally in the proximal-distal direction during fitting of the shaft;
to prevent tilting in the medial-lateral direction and also twisting of the shaft;
to seal off the gap occurring between the shaft and the femur in the proximal area so that pressure is exerted on the bone cement located in the medullary cavity.
The centering and/or sealing element has, in the proximal direction, an end face which is advantageously used as a reference surface. The centering and/or sealing element is preferably inserted into the medullary cavity in such a way that said reference surface is flush with the resected surface of the femoral neck. The endoprosthesis shaft is secured on a fitting instrument prior to insertion, a spacer element additionally being secured on the fitting instrument, said spacer element being designed in such a way that with the endoprosthesis shaft inserted deep in the medullary cavity, it lies on the reference surface of the centering and/or sealing element and prevents any further insertion of the shaft. By means of this spacer element which is available in different sizes, the depth of fitting of the endoprosthesis shaft can be adjusted exactly with respect to the resected surface. A spacer element corresponding to the desired depth of fitting is chosen and is secured on the fitting instrument prior to insertion of the endoprosthesis shaft.
A kit is understood as comprising the mutually adapted parts of centering and/or sealing element, endoprosthesis shaft and fitting instrument, if appropriate in combination with one or more spacer elements, and of this kit only the centering and/or sealing element and the endoprosthesis shaft are intended to remain as implants in the body.
A number of illustrative embodiments of the invention are described below with reference to figures, in which: